Mechanism and Kinetics of the Carbothermic Reduction of Metals in the FeS–Ni3S2–CaO System

Abstract

The reduction of metals by carbon and carbon monoxide in the FeS–Ni3S2–CaO system on continuous heating to 1250°C is studied using thermogravimetric and differential thermal analyses combined with mass spectrometry of gases. The formation of the oxysulfides CaFeSO and Ca3Fe4S3O6 along with sulfide phases is revealed in the FeS–CaO and FeS–Ni3S2–CaO systems on heating in an inert atmosphere. The chemism of the carbothermic reduction of sulfides FeS, Ni3S2, and Fe4.5Ni4.5S8 in a mixture with calcium oxide is determined. The reduction products are shown to be calcium sulfide and metals, and an additive of calcium oxide inhibits the evolution of sulfur-containing gases. The reduction of nickel sulfide by carbon and carbon monoxide is activated if iron sulfide is introduced into a reaction mixture along with calcium oxide. Iron sulfide favors the formation of intermediate iron–calcium oxysulfides with enhanced reactivity. In the temperature range from 750 to 1170°C, the experimental data on the carbothermic reduction of metals in the FeS‒Ni3S2–CaO system are described by a one-step Avrami–Erofeev model, in which the process is determined by the step of nuclei formation and growth. The kinetic parameters of the process are found to be E = 520 kJ/mol, log A = 18.2 s–1, and n = 0.87 (E is the activation energy, A is the preexponential factor, and n is the reaction order). The data obtained are useful for the development of technologies for the direct isolation of valuable metals from sulfide raw materials.